3GPP (3rd Generation Partnership Project) is a project in which the specification of a mobile phone system, based on a network that is evolved from W-CDMA (Wideband-Code Division Multiple Access) and GSM (Global System for Mobile Communications), is examined and prepared. In 3GPP, the W-CDMA scheme is standardized as the third generation cellular mobile communication scheme, and the service has been started one after another. Besides, HSDPA (High-Speed Downlink Packet Access) that is further improved in communication speed has been also standardized and the service has been started. In 3GPP, the evolution of the third generation radio accessing technology (Evolved Universal Terrestrial Radio Access: referred to hereinafter as “EUTRA”) has been investigated.
As the downlink communication scheme in EUTRA, an OFDMA (Orthogonal Frequency Division Multiple Access) scheme in which subcarriers orthogonal to each other are used to achieve user-multiplexing has been proposed. Further, in the OFDMA scheme, a technology called adaptive modulation and demodulation and error correction scheme (AMCS: Adaptive Modulation and Coding Scheme) based on adaptive radio link control (Link Adaptation) for channel coding etc. has been applied. AMCS is a scheme that switches radio transmission parameters (which will be referred to hereinbelow as AMC modes) such as an error correction method, error correction coding rate, data modulation level and so on, in accordance with the channel quality of each mobile station apparatus, in order to achieve efficient high-speed packet data transmission. The channel quality of each mobile station apparatus is fed back to a base station apparatus using CQI (Channel Quality Indicator).
In OFDMA, the communicatable domain can be divided into the frequency domains that physically correspond to subcarriers and the time domains. A set of several divided domains is called a resource block, and one or a number of resource blocks are assigned to each mobile station apparatus so as to perform multiplexing communication of plural mobile station apparatuses. In order to enable the base station apparatus and each mobile station apparatus to perform communication at the requested optimal quality and speed, it is necessary to determine assignment of resource blocks and a transmission scheme by considering the channel quality of the frequency band that corresponds to each subcarrier of each mobile station apparatus. Since the transmission scheme and scheduling are handled by the base station apparatus, in order to realize this request, the channel qualities for each frequency domain are fed back from each mobile station apparatus to the base station. Further, if necessary, information representing the frequency domains with high channel qualities may be fed back from each mobile station apparatus to the base station.
Furthermore, in EUTRA, in order to increase the channel capacity, use of transmission diversity such as SDM (Space Division Multiplexing: space multiplexing technology) by using MIMO (Multiple Input Multiple Output), SFBC (Space-Frequency Block Diversity), CDD (Cyclic Delay Diversity) has been proposed. The MIMO is the general term for multiple input/multiple output scheme or technologies, and is characterized by performing transmission by using multiple antennas at both the transmission side and reception side so as to pluralize the number of branches of wave input/output. The unit of signal sequences that can be transmitted by spatial multiplexing by using the MIMO scheme is called a stream. The number of streams (Rank) during MIMO communication is determined by the base station apparatus, taking into account the channel condition. The number of streams (Rank) requested by the mobile station apparatus is fed back from the mobile station apparatus to the base station apparatus, by using RI (Rank Indicator).
Further, in using SDM on downlink, in order to correctly separate information on multiple streams transmitted from individual antennas, it has been investigated that the transmission signal sequences are subjected to preprocessing (this is called precoding). The information on precoding is calculated based on the channel condition estimated by the mobile station apparatus, and is fed back from the mobile station apparatus to the base station apparatus by using PMI (Precoding Matrix Indicator).
In this way, in order to realize communication at the optimum quality, it is necessary to feed back various kinds of information that represents the channel condition, from each mobile station apparatus to the base station apparatus. This channel state information is made up of CQI, PMI, RI and the like. The number of bits and format of these pieces of channel state information are designated to the mobile station apparatus by the base station apparatus, depending on the circumstances.
Here, FIG. 11 shows a channel configuration in EUTRA. The downlink for EUTRA is configured of a downlink pilot channel DPiCH (Downlink Pilot Channel), a downlink synchronization channel PSCH (Physical Downlink Synchronization Channel), a downlink shared channel PDSCH (Physical Downlink Shared Channel), a downlink control channel PDCCH (Physical Downlink Control Channel), a downlink HARQ acknowledgement indicator channel PHICH (Physical HARQ Acknowledgement Indicator Channel) and a downlink broadcasting channel PBCH (Physical Broadcast Channel).
The uplink for EUTRA is configured of an uplink pilot channel UPiCH (Uplink Pilot Channel), a random access channel RACH (Random Access Channel), an uplink shared channel PUSCH (Physical Uplink Shared Channel) and an uplink control channel PUCCH (Physical Uplink Control Channel) (see non-patented document 1, for example).
In FIG. 12, the horizontal axis represents time and the vertical axis represents frequency. FIG. 12 shows the configuration of one radio frame. This radio frame is split into a plurality of radio resources. The domain of 1 ms wide in the temporal direction is called a subframe. The radio resources are given in units of a domain of 180 kHz wide in the frequency direction and 1 ms wide in the temporal direction, and PUSCH and PUCCH are assigned for these domains as shown in the drawing.
The channel state information is fed back by using PUCCH or PUSCH. The properties of the uplink single carrier make it impossible for the mobile station apparatus to transmit a plurality of channels simultaneously. PUCCH is used to transmit ACK (Positive Acknowledgement)/NACK (Negative Acknowledgement) used for HARQ (Hybrid Automatic Repeat Request) of downlink data and transmit channel state information.
PUSCH is mainly used to transmit uplink data. When the channel state information is not transmitted by PUCCH, the channel state information is transmitted together with the uplink data. In general, PUSCH has a greater resource assigned to transmit the channel state information within one subframe than PUCCH.
On the other hand, HARQ is applied for transmission of the uplink shared channel (PUSCH). In retransmitting of HARQ, there are two kinds of methods, one is chase combining in which retransmission identical to the previous transmission is transmitted and combined at the receiving side, and the other is incremental redundancy in which information which is not previously sent is additionally transmitted. The retransmission data is also generated from the same transport block from which new data was generated.
Now, FIG. 13 shows an uplink transmission procedure. In FIG. 13, the base station apparatus is depicted on the right side while the procedures of the mobile station apparatus are depicted on the left side.
Further, a subframe that the mobile station apparatus receives the data from the base station apparatus is called a downlink subframe (D-subframe) and a subframe that the mobile station apparatus transmits the data to the base station apparatus is called an uplink subframe (U-subframe).
Downlink subframes and uplink subframes are respectively depicted on the left and right sides in FIG. 13 for explanation. Here, the downlink subframe and the uplink subframe are not necessarily timed to each other.
To begin with, in order to transmit new data, an uplink grant is transmitted from the base station apparatus to the mobile station apparatus on PDCCH. The mobile station apparatus decodes on PDCCH to detect an uplink transmission grant signal (the uplink grant) to the mobile station apparatus (D-subframe #2).
This uplink grant includes a new data indicator that indicates new data. Then, after a fixed processing time associated with D-subframe #2 (uplink subframe U-subframe #6), the uplink data (new data) is transmitted on PUSCH.
The base station apparatus performs a decoding process of the uplink data and transmits a reply signal to the mobile station apparatus on PHICH. Specifically, the base station apparatus transmits to the mobile station apparatus by using PHICH, a positive reply (ACK) in case that CRC (Cyclic Redundancy Check) has succeeded, and a negative reply (NACK) in case that the CRC has failed.
Upon decoding PDCCH and PHICH at D-subframe #10, the mobile station apparatus detects no uplink grant on PDCCH, and detects NACK on PHICH, then retransmits the uplink data. In this case, transmission is performed using the same MCS and the same resource blocks as those used at the previous transmission.
This retransmission process is called a Non-Adaptive HARQ. The timing of the retransmission process in the uplink is synchronized. In this example, retransmissions are performed at intervals of 8 U-subframes. That is, the round-trip time is 8 subframes.
FIG. 14 shows an uplink transmission procedure of Adaptive HARQ. The base station apparatus performs a decoding process of the uplink data, and transmits ACK in case that the CRC (Cyclic Redundancy Check) has succeeded and the uplink grant included with information for retransmission in case that the CRC has failed, in order to designate new MCS and resource blocks for retransmission.
The mobile station apparatus decodes on PDCCH at D-subframe #10, and retransmits the uplink data when the uplink grant has been detected on PDCCH. In this case, transmission is performed by using new MCS and resource blocks that are designated by using PDCCH. This retransmission process is called an Adaptive HARQ.
Further, non-patented document 2 proposes a method of transmitting the channel state information from the mobile station apparatus to the base station apparatus, in which the base station apparatus uses the uplink grant including information that designates transmission of the channel state information on PUSCH, in order to transmit the channel state information aperiodically (trigger-wise). The mobile station apparatus, having received the uplink grant including information that designates the transmission of the channel state information, transmits detailed channel state information by using the assigned resources, whereby flexible transmission and reception of the channel state information is realized between the base station apparatus and the mobile station apparatus.
Moreover, non-patented document 3 proposes a method of transmitting the channel state information from the mobile station apparatus to the base station apparatus, in which when the base station apparatus assigns resources on PUSCH, the channel state information is continuously transmitted so as to realize frequent the transmission of detailed channel state information without use of any special signaling.    Non-patented document 1: 3GPP TS (Technical Specification) 36.211, V1.10 (2007-05), Technical Specification Group Radio Access Network, Physical Channel and Modulation (Release 8)    Non-patented document 2: “CQI Trigger Mechanism”, 3GPP TSG RAN WG1 Meeting #50bis, R1-074353, October 2007    Non-patented document 3: “Channel feedback format selection”, 3GPP, TSG RAN WG1 Meeting #51, R1-974854, November 2007